Large fluctuations in gas and/or liquid production can lead to major disruptions on the topside facilities. Level control of separators becomes difficult with the risk of liquid carry-over into the gas train. Furthermore, the pressure surges accompanying the liquid surges hamper the gas compression facilities. These fluctuations are caused by the fluid composition, geometrical layout and operating conditions of the production system. Especially with flowline/riser systems, the riser may have a large impact on the amplitude of the production fluctuations.
With the current trends of producing from marginal gas/condensate and oil fields to existing facilities with subsea tie-backs, the development of more deepwater fields and producing from existing production facilities towards the end of field life cycle issues with irregular production or slugging pipeline systems are observed more frequently.
The most recent technology in Shell for slug control is the Smart Choke. This technology consists of a single control valve that is installed between the riser top and the first stage separator. It is an active slug control device, and, therefore, continuous acting on changes in the flow of gas and liquid by manipulating the opening of the control valve.
Smart Chokes have been installed in the Gulf of Mexico (GoM) and in Malaysia. The flowlines were experiencing large fluctuations in liquid and gas production and pressure fluctuations at the inlet of the flowline and at the outlet of the riser, which were caused by a hydraulically unstable flowline/riser system.
Case histories of deployments in the GoM – as well as recent assessments for Shell UK, Malaysia and Nigeria – indicate (potential) production gains of about 5–10%. Also, the technology is used to extend field life. In end of field life, the pipeline is often over dimensioned because of the lower gas rates and increased water production. These conditions may lead to surges, which are too large to be handled by production facilities and may lead to an early abandonment of the pipeline with the connected well(s).